Yes, socialization is very important. Even if the kittens hide at first, letting them hear non-threatening human voices will help.
How old do you think they are? From the pictures, I can tell that they aren't tiny babies. My wild guess would be 10-12 weeks old, so kitten milk replacer is probably unnecessary. I'd go with a good quality dry kitten chow for a balanced diet, maybe canned food once a day, and the suggested baby meat as a treat to get them to associate you with Good Things, not the main component of their diet. Do NOT give them cows' milk right away. Many cats have diarrhea if they drink cows' milk, and their little tummies will have enough to do to adjust from mice to dry food.
(As an aside, meat baby food is one of those things that even a seriously ill cat will eat, even if they're refusing other foods.)
How fast they tame down may come down to their own personalities. The stray kitten currently sleeping in my downstairs bathroom was reported to be a feral, but if so he's the most people-loving feral I've ever heard of!